The present invention relates to a dielectric resonator and also to a filter employing the dielectric resonator.
In FIG. 1, the principle of a conventional filter provided with a disc type dielectric resonator 2 which is formed by ceramic material of the titanium dioxide (TiO.sub.2) family is schematically illustrated. A reference numeral 4 designates a metal casing, and the resonator 2 is hermetically disposed in the casing 4 approximately at a center portion by a support 6, also made of ceramics, such as forsterite. The operation mode is TE.sub.01.delta.. A coupling circuit includes an input means and an output means which are diagrammatically shown at 8 and 10. The size of the casing 4, particularly the dimension of the internal space is so arranged as to produce a cut-off condition at a dominant frequency. It is to be noted that the resonator 2 which is shown as having a disc shape can be arranged in a shape of a doughnut or in a shape of a polygon prism. Furthermore, the support 6 can be formed by an electrically non-conductive substrate. An external circuit (not shown) which is to be connected to the coupling circuit can be any known circuit, i.e., waveguide circuit, coaxial circuit or MIC circuit. Although the above described type of resonator has a high Q-factor, there are several disadvantages as follows;
(i) In the field of electronic parts and devices, many approaches have been made to reduce their size, and from this point of view, the size of the conventional filter is still bulky. This is due to the large configuration of the dielectric resonator, which accordingly increases the size of the casing. PA1 (ii) When used in a high power circuit, the resonator generates a large amount of heat which is not completely transmitted to the casing, and accordingly, the temperature of the resonator increases. This results in deviation of resonant frequency and/or reduction of Q-factor.